1. Field of Invention
The present invention relates to a method and apparatus for processing video images.
2. Background
In order to enhance a viewer's experience when watching video material, it is possible to apply known techniques in order to give a viewer the impression that certain images within the video material have a three dimensional (3D) quality. This is achieved by arranging the video to include a sequence of stereoscopic images in which a viewer sees a first image through one eye and a second image through the other eye. If the first image and the second image are of the same object but the images are horizontally displaced from each other with respect to the viewing plane that the viewer sees (e.g. a television display or a cinema screen), then the viewer reconciles this visual information by perceiving there to be a single image of the object and that this image has a certain degree of depth (i.e. is positioned either in front of or behind the viewing plane). The 3D effect can be enhanced by arranging the two images to be of the same object but captured from slightly different angles. Because human eyes are spaced apart by a small distance, this mimics the information that a viewer sees when a real object is viewed through both eyes thus the viewer perceives the displayed image as a 3D object.
Unlike conventional two-dimensional (2D) video sequences, in order for a viewer to view a 3D image, their eyes must be pointing in slightly different directions due to the horizontal displacement of the displaced version of the same object. When viewing stereoscopic images, unnatural movement of the viewer's eyes can take place. For instance, a viewer's eyes may unnaturally diverge, may converge too much or may vertically diverge (as a result of vertical parallax in the images). This can lead to discomfort. It can therefore be useful to analyse 3D video sequences to determine the extent to which a viewer must point their eyes in different directions by producing a disparity map which indicates the relative position of the first and second object.
Furthermore, when combining the display of 2D images with 3D images in a video sequence, careful considerations must be made to ensure that the 3D illusion does not break down. This is particularly important in live footage where objects in the footage may move “through” the captions.